Bracken T, Senior Russell, Dudman Joseph
T. Dan Bracken, Inc., Portland, OR 97282, USA.
J Occup Environ Hyg. 2005 Sep;2(9):444-55. doi: 10.1080/15459620591034646.
This article reports on an investigation of 60-Hz electric-field exposures of line workers in 230- to 765-kV transmission line towers. The exposures were based on computations of the unperturbed electric field along climbing routes and at work positions on the towers and on insulated ladders suspended in towers. Computed exposures were expressed in terms of the unperturbed electric field averaged over the body as stipulated by guidelines. For the realistic on-tower positions, the worker's posture, the uniformity of the field, and the field orientation differed from the guideline exposure scenario of standing erect in a vertical uniform field. These differences suggest the need for care in comparing electric-field exposures in towers with guideline limits. The unperturbed nonuniform fields at discrete points near steel and aluminum lattice structures were computed using Monte Carlo methods that model surface and spatial electric fields on and near standard geometrical elements. To estimate a whole-body average, fields were computed at 10 discrete points positioned on segments of an articulated stick-figure model of the human body. The whole-body average field was computed from fields at all the points weighted by the fraction of body volume that the corresponding segment represented. We estimated the average unperturbed electric field, the space potential at the torso, and the induced short-circuit current for 19 climbing and work positions in six towers. The maximum average electric-field exposure during climbing ranged from 10 kV/m for a 230-kV tower to 31 kV/m for a 765-kV tower. Exposures at on-tower work positions were lower than the estimated maximum exposures during climbing. For 500- and 765-kV towers, computed exposures while climbing and at some on-tower positions exceeded the limit of 20 kV/m given in the recently adopted IEEE Standard C95.6 2002. For lower voltage towers, exposures did not exceed 20 kV/m.
本文报道了对230至765千伏输电线路塔上线路工人60赫兹电场暴露情况的调查。这些暴露情况是基于沿攀爬路线、塔上工作位置以及塔中悬挂的绝缘梯上未受干扰的电场计算得出的。计算出的暴露量按照指南规定以身体上未受干扰的平均电场来表示。对于实际的塔上位置，工人的姿势、电场的均匀性以及电场方向与指南中直立于垂直均匀电场中的暴露场景有所不同。这些差异表明在将塔上的电场暴露与指南限值进行比较时需要谨慎。使用蒙特卡罗方法计算了靠近钢和铝格构结构的离散点处未受干扰的非均匀电场，该方法对标准几何元素及其附近的表面和空间电场进行建模。为了估计全身平均值，在人体关节式简笔画模型的各段上的10个离散点处计算电场。全身平均电场是根据所有点处的电场，按照相应段所代表的身体体积比例加权计算得出的。我们估计了六座塔中19个攀爬和工作位置的平均未受干扰电场、躯干处的空间电位以及感应短路电流。攀爬过程中的最大平均电场暴露量，对于230千伏的塔为10千伏/米，对于765千伏的塔为31千伏/米。塔上工作位置的暴露量低于攀爬过程中估计的最大暴露量。对于500千伏和765千伏的塔，计算得出的攀爬过程中和某些塔上位置的暴露量超过了最近采用的IEEE标准C95.6 2002中规定的20千伏/米的限值。对于较低电压的塔，暴露量未超过20千伏/米。
